#include <iostream>
#include <cmath>
using namespace std;

double arctanx(double x) {
    double res = x;
    int i = 2;
    while(pow(x, 2*i-1)*1.0 / (2*i-1) > pow(10, -6))
    {
        double val = pow(x, 2*i-1)*1.0 / (2*i-1);
        if (i % 2 == 1)
        {
            res += val;
        } else {
            res -= val;
        }
        i++;
    }
    return res;
}

int main() {
    
    double pai = 6 * arctanx(1.0/sqrt(3));
    printf("%.10f", pai);
    return 0;
}